Technical Abstract:
Keeping cattle fever ticks (CFT), Rhipicephalus (Boophilus) microplus and R. annulatus, eradicated from the United States and thus keeping the national cattle herd free of bovine babesiosis is a current and critical agricultural biosecurity issue of national relevance. Also known as “Texas fever”, bovine babesiosis remains foreign to the U.S., but it is a reportable disease according to the World Organization for Animal Health. It is estimated that the livestock industry realizes annual savings of at least 3 billion dollars since the U.S. was declared free of the ticks and bovine babesiosis. However, global change is impacting the ability of state and federal agencies to keep the national herd free of CFT (George 2008). Bovine babesiosis outbreaks in the U.S. are a real and imminent risk to the cattle industry perhaps due to shifts in the ecology of wild ungulate hosts that may support the maintenance and dissemination of CFT. During our presentation we will discuss the dynamics of factors influencing the apparent spread of CFT back into South Texas and immediate actions that can be taken to address this threat to the national food supply and prevent them from spreading back into their previous range in the U.S.
The eradication of bovine babesiosis from the U.S. represents a very successful campaign in the history of disease eradication efforts. Babesia bovis and B. bigemina are the etiologic agents of bovine babesiosis, and B. bovis is considered the most economically important arthropod-borne pathogen of livestock worldwide (Bock et al. 2004). Following his decisive studies done in collaboration with Frederick L. Kilborne leading to our understanding of how the disease was transmitted to cattle by CFT, Theobald Smith stated, “Eliminate the ticks on cattle and you eradicate the ticks because they cannot live elsewhere” (Ojan and Stanek 2002). Thus, systematic dipping of cattle in vats containing an acaricide was the cornerstone of the Cattle Fever Tick Eradication Program, which was created in 1906. CFT were declared eradicated from the U.S. in 1943 with the exceptions of a persistent population in Florida that was eradicated in the early 1960’s and the permanent quarantine zone along the border with Mexico in South Texas that remains in place today (Bram and George 2000).
The number of CFT outbreaks within and outside the permanent quarantine zone fluctuates with time. A significant incursion of CFT took place in the 1970s. Of a total of 170 outbreaks recorded in 1973, 112 occurred outside of the permanent quarantine zone. It took six years to re-eradicate the ticks. Once again, the level of CFT activity in the U.S. has increased to alarming levels during the last five years. The largest number of infested premises in the permanent quarantine zone was initially recorded in 2005, but that record was broken again in 2008 when CFT were detected in 85 premises (Table 1). A sustained spillover of CFT into the free zone also has been noted since 2004. This situation triggered the establishment of preventive quarantines by the Texas Animal Health Commission and the U.S. Department of Agriculture Animal and Plant Health Inspection Service – Veterinary Services to try to contain the CFT and eventually re-eradicate them from the U.S. In June 2009 the number of CFT outbreaks outside the permanent quarantine surpassed the total in 2008 and a zone covering almost a million acres was established under preventive quarantine in South Texas.
Native and non-native species of wild ungulates figure prominently among the likely causes for the apparent re-invasion of the U.S. by CFT. Among them, white-tailed deer are regarded as the major complicating factor in eradication efforts since they are suitable hosts for CFT. CFT eradication in pastures vacated of cattle was considered impossible as long as white-tailed deer remained within an area (Shillinger 1938). Approximately 20,000 white-tailed deer had to be culled (Hourrigan, unpublished data) before CFT eradication in Florida was officially completed in 1961 (Bram and George 2000). In the absence of cattle as the preferred host, white-tailed deer and some species of non-native wild ungulates appear to fill in the ecological niche as hosts for CFT in rangeland and pastures. In South Texas the complexities of this situation are compounded by agricultural practices as well as environmental and ecological conditions promoting the abundance of white-tailed deer and non-native ungulates. For example, the use of land for non-native pasture in Starr and Zapata Counties decreased significantly or remained non-existent whereas native rangeland increased substantially or decreased slightly, respectively (Figures 1 and 2). The majority of CFT outbreaks within and outside the permanent quarantine zone in 2009 have occurred in Starr and Zapata Counties. Additionally, it has been documented through hunter-killed surveillance in Zapata and Starr Counties that during fiscal year 2009 at least 46% of all the CFT infestation in the permanent quarantine zone occurred in white-tailed deer. This finding correlates with recent catch and release campaigns by the USDA Agricultural Research Service, APHIS-VS, and TAHC. These campaigns have documented consistently that white-tailed deer (family: Cervidae) in South Texas are infested with CFT. In March 2009 nilgai antelope (family: Bovidae) were culled in the Lower Rio Grande Valley National Wildlife Refuge near Boca Chica in Cameron County, TX; four of the seventeen nilgai inspected were infested with CFT. Nilgai were reported to be infected with Babesia spp. in India (Baviskar et al. 2009) and in Mexico where they were found to be exposed to B. bovis and B. bigemina (Cárdenas-Canales et al. Unpublished data). It was noted in 1941 that white-tailed deer mingling freely with regularly dipped cattle were not infested with CFT (Travis 1941). Controlled and regulated research using cattle as a sentinel species may help cattle producers and regulatory agencies to make science-based mitigation decisions or support predictive capabilities for the CFT eradication program as suggested for other species as sentinels of ecological health (Alonso Aguirre 2009).
The USDA-ARS held a workshop at McAllen, TX addressing emergency research on cattle fever tick and bovine babesiosis in April 2009. Cattle producers, representatives of federal and state agencies, the animal health industry, and academicians from the U.S. and Mexico attended the workshop. Following a full day of presentations, participants formed groups to address issues related to integrated tick eradication, epidemiology and surveillance, tick vaccines, and diagnostics with the goal to identify short- and long-term research and development initiatives for sustainable and effective CFT eradication. The workshop was a reflection of the One Health Initiative since it included the participation of experts in human babesiosis. This presentation will include an update on outcomes from the workshop.
Other ongoing initiatives include the USDA-Natural Resources Conservation Service Environmental Quality Incentives Program (EQIP) for the Rio Grande Domestic Animal Stress/Mortality Statewide Resource Concern and the APHIS-VS Game Fencing Initiative. Through EQIP, the NRCS provides technical and financial assistance to ranchers in a 17-county area of South Texas to help fight the spread of CFT. Livestock producers can voluntarily work with their local NRCS and soil and water conservation district to develop a conservation plan with land management practices that help them meet their land management goals and objectives. The producers will also receive technical assistance to implement the conservation plan and, in installing land management practices, to fight the spread of CFT. The purpose of the Game Fencing Initiative is to fill in the wild game gaps of the permanent quarantine zone line to prevent movement of